Chapter 21

What are the main topics covered in the lecture on lipid metabolism?

Fatty Acid Biosynthesis, Desaturases, Oxidases, Eicosanoids, Triacylglycerol (TAG) Synthesis, Phospholipids Synthesis, Cholesterol Biosynthesis.

What is the role of Acetyl-CoA Carboxylase (ACC) in fatty acid biosynthesis?

ACC converts acetyl-CoA and bicarbonate into malonyl-CoA, which is essential for synthesizing fatty acids.

List the four main steps in fatty acid synthesis.

1. Condensation, 2. Reduction, 3. Dehydration, 4. Reduction.

What are the two types of Fatty Acid Synthase (FAS) and where are they found?

FAS I is found in vertebrates and fungi, producing mainly palmitate; FAS II is found in plants and bacteria, producing diverse fatty acids.

Where does fatty acid biosynthesis occur?

In the cytosol of adipocytes, hepatocytes, and mammary glands.

How is Acetyl-CoA transported from mitochondria to the cytosol?

Citrate transports acetyl-CoA from mitochondria to the cytosol.

What activates and inhibits Acetyl-CoA Carboxylase (ACC)?

Activated by citrate and ATP; inhibited by palmitoyl-CoA, glucagon, and epinephrine.

What is the main function of desaturases in fatty acid metabolism?

Desaturases introduce double bonds into fatty acids, affecting their saturation.

What are eicosanoids derived from?

Arachidonic acid (20:4), produced in response to stimuli like inflammation.

What is the function of cyclooxygenase (COX) enzymes?

COX enzymes convert arachidonate to prostaglandins, thromboxanes, and leukotrienes.

What regulates cholesterol biosynthesis?

HMG-CoA reductase is the rate-limiting enzyme, regulated by feedback inhibition, phosphorylation, and proteolytic degradation.

What are the fates of cholesterol in the body?

Cholesterol is used in membranes, bile acids, steroid hormones, and transported via lipoproteins.

What is the role of HDL in cholesterol transport?

HDL returns excess cholesterol to the liver for disposal, having a protective role in cardiovascular disease.

What happens to VLDL after losing triacylglycerols (TAGs)?

They become LDL (Low-Density Lipoproteins) which deliver cholesterol to tissues.

What are the consequences of high levels of LDL cholesterol?

High LDL levels are associated with atherosclerosis and heart disease.

What is the role of malonyl-CoA in fatty acid synthesis?

Malonyl-CoA serves as the carbon donor in the fatty acid synthesis pathway.

What are the key substrates for fatty acid biosynthesis?

The key substrates are acetyl-CoA, malonyl-CoA, and reducing equivalents (NADPH).

What is the significance of palmitate in lipid metabolism?

Palmitate (16:0) is the primary fatty acid produced during fatty acid synthesis and serves as a precursor for other fatty acids.

What is the relationship between eicosanoids and inflammation?

Eicosanoids, derived from arachidonic acid, play crucial roles in mediating inflammatory responses.

How does insulin affect fatty acid metabolism?

Insulin promotes fatty acid synthesis by activating Acetyl-CoA Carboxylase (ACC) and inhibiting lipolysis.

What is the function of lipoprotein lipase (LPL)?

LPL hydrolyzes triacylglycerols (TAGs) in blood lipoproteins, facilitating fat uptake by tissues.

What are the different types of eicosanoids?

Eicosanoids include prostaglandins, thromboxanes, and leukotrienes, all synthesized from arachidonic acid.

What enzyme catalyzes the first step of cholesterol biosynthesis?

HMG-CoA reductase catalyzes the conversion of HMG-CoA to mevalonate, the first committed step in cholesterol biosynthesis.

How does the body excrete cholesterol?

Cholesterol is excreted primarily in bile as bile acids and salts, and as free cholesterol in bile.

What impact does dietary fat have on heart health?

Dietary fat composition can influence heart health; unsaturated fats are beneficial, while trans fats and saturated fats can increase heart disease risk.

What is the role of phospholipids in cell membranes?

Phospholipids form the bilayer of cell membranes, providing structural integrity and fluidity.

How are triacylglycerols (TAGs) formed?

TAGs are formed by the esterification of glycerol with three fatty acids.

What is the function of cholesterol in membranes?

Cholesterol helps maintain membrane fluidity and stability across varying temperatures.

What are the main regulatory mechanisms of HMG-CoA reductase?

HMG-CoA reductase is regulated by cholesterol levels, phosphorylation, and regulatory proteins.

What is the significance of omega-3 fatty acids?

Omega-3 fatty acids have anti-inflammatory properties and are important for cardiovascular health.

What is the process of lipolysis?

Lipolysis is the breakdown of stored triacylglycerols into free fatty acids and glycerol, primarily in adipose tissue.

What are key dietary sources of essential fatty acids?

Key sources include fish, flaxseeds, walnuts, and chia seeds.

What is the function of very-low-density lipoproteins (VLDL)?

VLDL transports lipids, primarily triacylglycerols, from the liver to peripheral tissues.

How do eicosanoids influence cardiovascular function?

Eicosanoids regulate vascular tone, platelet aggregation, and inflammatory responses, impacting cardiovascular health.

What is the role of chylomicrons in fat metabolism?

Chylomicrons transport dietary lipids from the intestines to other locations in the body for energy or storage.